DNA damage response in peripheral mouse blood leukocytes in vivo after variable, low-dose rate exposure

Environmental contamination and ingestion of the radionuclide Cesium-137 (137Cs) is a large concern in fallout from a nuclear reactor accident and improvised nuclear device and highlights the need to develop biological assays for low dose rate, internal emitter radiation. To mimic low dose rates attributable to fallout, we have developed a VAriable Dose-rate External 137Cs irradiatoR (VADER), which can provide arbitrarily varying and progressive low dose rate irradiations in the range of 1.2 to 0.1 Gy/day, while circumventing the complexities of dealing with radioactively-contaminated biomaterials. We investigated the kinetics of mouse peripheral leukocytes DNA damage response in vivo after variable, low-dose rate 137Cs exposure. C57BL/6 mice were placed in the VADER over 7 days with total accumulated dose up to 2.7 Gy. Peripheral blood response including the leukocytes depletion, apoptosis signal protein p53 and DNA repair biomarker {gamma}-H2AX were measured. The results illustrated that blood leukocyte count had significantly dropped by days 7. P53 levels peaked at day 2 (total dose=0.91Gy) and then declined whereas {gamma}-H2AX yields generally increased with accumulated dose and peaked at day 5 (total dose=2.08Gy). ROC curve analysis for {gamma}-H2AX provided a good discrimination of accumulated dose < 2 Gy and [≥] 2 Gy, highlighting the potential of {gamma}-H2AX as a biomarker dosimetry in a protracted, environmental exposure scenario.